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                <h1 id="EverydayOneCat"><a href="#EverydayOneCat" class="headerlink" title="EverydayOneCat"></a>EverydayOneCat</h1><p>新年新气象ヽ(✿ﾟ▽ﾟ)ノ！！！</p>
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<h1 id="MyBatisPlus简介"><a href="#MyBatisPlus简介" class="headerlink" title="MyBatisPlus简介"></a>MyBatisPlus简介</h1><h2 id="一、简介"><a href="#一、简介" class="headerlink" title="一、简介"></a>一、简介</h2><p>官网：<a target="_blank" rel="noopener" href="http://mp.baomidou.com/">http://mp.baomidou.com/</a></p>
<p>参考教程：<a target="_blank" rel="noopener" href="http://mp.baomidou.com/guide/">http://mp.baomidou.com/guide/</a></p>
<p><a target="_blank" rel="noopener" href="https://github.com/baomidou/mybatis-plus">MyBatis-Plus</a>（简称 MP）是一个 <a target="_blank" rel="noopener" href="http://www.mybatis.org/mybatis-3/">MyBatis</a> 的增强工具，在 MyBatis 的基础上只做增强不做改变，为简化开发、提高效率而生。</p>
<h2 id="二、特性"><a href="#二、特性" class="headerlink" title="二、特性"></a>二、特性</h2><ul>
<li><strong>无侵入</strong>：只做增强不做改变，引入它不会对现有工程产生影响，如丝般顺滑</li>
<li><strong>损耗小</strong>：启动即会自动注入基本 CURD，性能基本无损耗，直接面向对象操作</li>
<li><strong>强大的 CRUD 操作</strong>：内置通用 Mapper、通用 Service，仅仅通过少量配置即可实现单表大部分 CRUD 操作，更有强大的条件构造器，满足各类使用需求</li>
<li><strong>支持 Lambda 形式调用</strong>：通过 Lambda 表达式，方便的编写各类查询条件，无需再担心字段写错</li>
<li><strong>支持多种数据库</strong>：支持 MySQL、MariaDB、Oracle、DB2、H2、HSQL、SQLite、Postgre、SQLServer2005、SQLServer 等多种数据库</li>
<li><strong>支持主键自动生成</strong>：支持多达 4 种主键策略（内含分布式唯一 ID 生成器 - Sequence），可自由配置，完美解决主键问题</li>
<li><strong>支持 XML 热加载</strong>：Mapper 对应的 XML 支持热加载，对于简单的 CRUD 操作，甚至可以无 XML 启动</li>
<li><strong>支持 ActiveRecord 模式</strong>：支持 ActiveRecord 形式调用，实体类只需继承 Model 类即可进行强大的 CRUD 操作</li>
<li><strong>支持自定义全局通用操作</strong>：支持全局通用方法注入（ Write once, use anywhere ）</li>
<li><strong>支持关键词自动转义</strong>：支持数据库关键词（order、key……）自动转义，还可自定义关键词</li>
<li><strong>内置代码生成器</strong>：采用代码或者 Maven 插件可快速生成 Mapper 、 Model 、 Service 、 Controller 层代码，支持模板引擎，更有超多自定义配置等您来使用</li>
<li><strong>内置分页插件</strong>：基于 MyBatis 物理分页，开发者无需关心具体操作，配置好插件之后，写分页等同于普通 List 查询</li>
<li><strong>内置性能分析插件</strong>：可输出 Sql 语句以及其执行时间，建议开发测试时启用该功能，能快速揪出慢查询</li>
<li><strong>内置全局拦截插件</strong>：提供全表 delete 、 update 操作智能分析阻断，也可自定义拦截规则，预防误操作</li>
<li><strong>内置 Sql 注入剥离器</strong>：支持 Sql 注入剥离，有效预防 Sql 注入攻击</li>
</ul>
<h1 id="MyBatisPlus快速开始"><a href="#MyBatisPlus快速开始" class="headerlink" title="MyBatisPlus快速开始"></a>MyBatisPlus快速开始</h1><h2 id="1-创建并初始化数据库"><a href="#1-创建并初始化数据库" class="headerlink" title="1.创建并初始化数据库"></a>1.创建并初始化数据库</h2><p>创建测试数据库mybatis_plus及测试表User</p>
<p>建表SQL如下:</p>
<pre class="line-numbers language-sql" data-language="sql"><code class="language-sql">CREATE TABLE user
(
	id BIGINT(20) NOT NULL COMMENT '主键ID',
	name VARCHAR(30) NULL DEFAULT NULL COMMENT '姓名',
	age INT(11) NULL DEFAULT NULL COMMENT '年龄',
	email VARCHAR(50) NULL DEFAULT NULL COMMENT '邮箱',
	PRIMARY KEY (id)
);

INSERT INTO user (id, name, age, email) VALUES
(1, 'Jone', 18, 'test1@baomidou.com'),
(2, 'Jack', 20, 'test2@baomidou.com'),
(3, 'Tom', 28, 'test3@baomidou.com'),
(4, 'Sandy', 21, 'test4@baomidou.com'),
(5, 'Billie', 24, 'test5@baomidou.com');<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>其表结构如下：</p>
<div class="table-container">
<table>
<thead>
<tr>
<th>id</th>
<th>name</th>
<th>age</th>
<th>email</th>
</tr>
</thead>
<tbody>
<tr>
<td>1</td>
<td>Jone</td>
<td>18</td>
<td>test1@baomidou.com</td>
</tr>
<tr>
<td>2</td>
<td>Jack</td>
<td>20</td>
<td>test2@baomidou.com</td>
</tr>
<tr>
<td>3</td>
<td>Tom</td>
<td>28</td>
<td>test3@baomidou.com</td>
</tr>
<tr>
<td>4</td>
<td>Sandy</td>
<td>21</td>
<td>test4@baomidou.com</td>
</tr>
<tr>
<td>5</td>
<td>Billie</td>
<td>24</td>
<td>test5@baomidou.com</td>
</tr>
</tbody>
</table>
</div>
<h2 id="2-初始化工程"><a href="#2-初始化工程" class="headerlink" title="2.初始化工程"></a>2.初始化工程</h2><p>创建一个Springboot测试工程，pom文件：</p>
<pre class="line-numbers language-markup" data-language="markup"><code class="language-markup"><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>parent</span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">&gt;</span></span>org.springframework.boot<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">&gt;</span></span>spring-boot-starter-parent<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>version</span><span class="token punctuation">&gt;</span></span>2.2.1.RELEASE<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>version</span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>relativePath</span><span class="token punctuation">/&gt;</span></span> <span class="token comment">&lt;!-- lookup parent from repository --&gt;</span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>parent</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">&gt;</span></span>com.atguigu<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">&gt;</span></span>mybatisplus<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>version</span><span class="token punctuation">&gt;</span></span>1.0-SNAPSHOT<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>version</span><span class="token punctuation">&gt;</span></span>


<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>dependencies</span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>dependency</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">&gt;</span></span>org.springframework.boot<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">&gt;</span></span>spring-boot-starter<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>dependency</span><span class="token punctuation">&gt;</span></span>

    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>dependency</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">&gt;</span></span>org.springframework.boot<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">&gt;</span></span>spring-boot-starter-test<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>scope</span><span class="token punctuation">&gt;</span></span>test<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>scope</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>exclusions</span><span class="token punctuation">&gt;</span></span>
            <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>exclusion</span><span class="token punctuation">&gt;</span></span>
                <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">&gt;</span></span>org.junit.vintage<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">&gt;</span></span>
                <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">&gt;</span></span>junit-vintage-engine<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">&gt;</span></span>
            <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>exclusion</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>exclusions</span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>dependency</span><span class="token punctuation">&gt;</span></span>

    <span class="token comment">&lt;!--mybatis-plus--&gt;</span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>dependency</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">&gt;</span></span>com.baomidou<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">&gt;</span></span>mybatis-plus-boot-starter<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>version</span><span class="token punctuation">&gt;</span></span>3.0.5<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>version</span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>dependency</span><span class="token punctuation">&gt;</span></span>

    <span class="token comment">&lt;!--mysql--&gt;</span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>dependency</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">&gt;</span></span>mysql<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">&gt;</span></span>mysql-connector-java<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>dependency</span><span class="token punctuation">&gt;</span></span>

    <span class="token comment">&lt;!--lombok用来简化实体类--&gt;</span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>dependency</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">&gt;</span></span>org.projectlombok<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">&gt;</span></span>lombok<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>dependency</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>dependencies</span><span class="token punctuation">&gt;</span></span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>创建配置文件application.properties：</p>
<pre class="line-numbers language-properties" data-language="properties"><code class="language-properties">spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/mybatis_plus?serverTimezone=GMT%2B8
spring.datasource.username=root
spring.datasource.password=123456<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span></span></code></pre>
<blockquote>
<p>1、这里的 url 使用了 ?serverTimezone=GMT%2B8 后缀，因为Spring Boot 2.1 集成了 8.0版本的jdbc驱动，这个版本的 jdbc 驱动需要添加这个后缀，否则运行测试用例报告如下错误：</p>
<p>java.sql.SQLException: The server time zone value ‘ÖÐ¹ú±ê×¼Ê±¼ä’ is unrecognized or represents more </p>
<p>2、这里的 driver-class-name 使用了 com.mysql.cj.jdbc.Driver ，在 jdbc 8 中 建议使用这个驱动，之前的 com.mysql.jdbc.Driver 已经被废弃，否则运行测试用例的时候会有 WARN 信息</p>
</blockquote>
<p>创建包 entity 编写实体类 <code>User.java</code></p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">@Data
public class User {
    private Long id;
    private String name;
    private Integer age;
    private String email;
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<h2 id="3-入门案例"><a href="#3-入门案例" class="headerlink" title="3.入门案例"></a>3.入门案例</h2><p>在Mybatis中我们需要创建mapper包编写接口并在resource中创建同名包编写对应的XML文件</p>
<p>而Mybatis_Plus则帮我们简化了这一步骤，我们只需要将接口继承BaseMapper&lt;&gt;类即可：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">public interface UserMapper extends BaseMapper&lt;User&gt; {
    
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span></span></code></pre>
<p>同时，我们需要在主启动类添加注解<code>@MapperScan</code> ，扫描 Mapper 文件夹</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">@MapperScan("com.atguigu.mapper")<span aria-hidden="true" class="line-numbers-rows"><span></span></span></code></pre>
<p>添加测试类，进行功能测试：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">@SpringBootTest
public class MybatisPlusApplicationTests {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testSelectList() {
        System.out.println(("----- selectAll method test ------"));
        //UserMapper 中的 selectList() 方法的参数为 MP 内置的条件封装器 Wrapper
        //所以不填写就是无任何条件
        List&lt;User&gt; users = userMapper.selectList(null);
        users.forEach(System.out::println);
    }
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>经测试我们发现通过以上几个简单的步骤，我们就实现了 User 表的 CRUD 功能，甚至连 XML 文件都不用编写！</p>
<h2 id="4-配置日志"><a href="#4-配置日志" class="headerlink" title="4.配置日志"></a>4.配置日志</h2><p>我们可以在配置文件中新增一个配置来运用MybatisPlus查看sql输出日志</p>
<pre class="line-numbers language-properties" data-language="properties"><code class="language-properties">#mybatis日志
mybatis-plus.configuration.log-impl=org.apache.ibatis.logging.stdout.StdOutImpl<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre>
<h1 id="MyBatisPlus的CRUD接口"><a href="#MyBatisPlus的CRUD接口" class="headerlink" title="MyBatisPlus的CRUD接口"></a>MyBatisPlus的CRUD接口</h1><h2 id="1-插入操作-主键策略"><a href="#1-插入操作-主键策略" class="headerlink" title="1.插入操作(主键策略)"></a>1.插入操作(主键策略)</h2><pre class="line-numbers language-java" data-language="java"><code class="language-java">@Test
public void testInsert(){
    User user = new User();
    user.setName("JY");
    user.setAge(18);
    user.setEmail("JY@qq.com");

    int result = userMapper.insert(user);
    System.out.println(result); //影响的行数
    System.out.println(user); //id自动回填
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>我们发现插入操作不需要我们指定主键，因为MybatisPlus默认会帮我们自动生成。</p>
<p>下面介绍几个常用的主键策略：</p>
<p><img src="https://pluto-1300780100.cos.ap-nanjing.myqcloud.com/img/6%20主键生成策略.png" alt="6 主键生成策略"></p>
<p>在MybatisPlus中，要想主键自增需要配置如下主键策略</p>
<ul>
<li>需要在创建数据表的时候设置主键自增</li>
<li>实体字段中配置 @TableId(type = IdType.AUTO)</li>
</ul>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">@TableId(type = IdType.AUTO)
private Long id;<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre>
<p>要想影响所有实体的配置，可以设置全局主键配置</p>
<pre class="line-numbers language-properties" data-language="properties"><code class="language-properties">#全局设置主键生成策略
mybatis-plus.global-config.db-config.id-type=auto<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre>
<h2 id="2-更新操作-自动填充"><a href="#2-更新操作-自动填充" class="headerlink" title="2.更新操作(自动填充)"></a>2.更新操作(自动填充)</h2><pre class="line-numbers language-java" data-language="java"><code class="language-java">@Test
public void testUpdateById(){

    User user = new User();
    user.setId(1L);
    user.setAge(28);

    int result = userMapper.updateById(user);
    System.out.println(result);

}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p><strong>注意：</strong>update时生成的sql自动是动态sql：UPDATE user SET age=? WHERE id=? </p>
<p>项目中经常会遇到一些数据，每次都使用相同的方式填充，例如记录的创建时间，更新时间等。</p>
<p>我们可以使用MyBatis Plus的自动填充功能，完成这些字段的赋值工作：</p>
<p><strong>（1）数据库表中添加自动填充字段</strong></p>
<p>在User表中添加datetime类型的新的字段 create_time、update_time</p>
<p><strong>（2）实体上添加注解</strong></p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">@Data
public class User {
    ......
        
    @TableField(fill = FieldFill.INSERT)
    private Date createTime;
    //@TableField(fill = FieldFill.UPDATE)
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime;
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p><strong>（3）实现元对象处理器接口</strong></p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">@Component
public class MyMetaObjectHandler implements MetaObjectHandler {
    @Override
    public void insertFill(MetaObject metaObject) {
        this.setFieldValByName("createTime",new Date(),metaObject);
        this.setFieldValByName("updateTime",new Date(),metaObject);
    }

    @Override
    public void updateFill(MetaObject metaObject) {
        this.setFieldValByName("updateTime",new Date(),metaObject);
    }
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>注意：不要忘记添加 @Component 注解</p>
<p>更新总结：</p>
<p><img src="https://pluto-1300780100.cos.ap-nanjing.myqcloud.com/img/8%20mp实现自动填充.png" alt="8 mp实现自动填充"></p>
<h2 id="3-乐观锁"><a href="#3-乐观锁" class="headerlink" title="3.乐观锁"></a>3.乐观锁</h2><p>Mysql中处理事务有两种锁法：悲观锁和乐观锁。</p>
<p>所谓悲观锁，就是当一个人执行这个事务时不允许其他人进行操作，类似于串行；而乐观锁相反，相当于并行，大大提高了效率。</p>
<p><strong>主要适用场景：</strong>当要更新一条记录的时候，希望这条记录没有被别人更新，也就是说实现线程安全的数据更新</p>
<p><strong>乐观锁实现方式：</strong></p>
<ul>
<li>取出记录时，获取当前version</li>
<li>更新时，带上这个version</li>
<li>执行更新时， set version = newVersion where version = oldVersion</li>
<li>如果version不对，就更新失败</li>
</ul>
<p><img src="https://pluto-1300780100.cos.ap-nanjing.myqcloud.com/img/9%20乐观锁.png" alt="9 乐观锁"></p>
<p><strong>（1）数据库中添加version字段（初始值为1）</strong></p>
<p><strong>（2）实体类添加version字段并添加 @Version 注解</strong></p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">@Version
private Integer version;<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre>
<p><strong>（3）在 配置类 中注册 乐观锁插件Bean</strong></p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">@Configuration
@MapperScan("com.atguigu.mybatis_plus.mapper")
public class MybatisPlusConfig {

    /**
     * 乐观锁插件
     */
    @Bean
    public OptimisticLockerInterceptor optimisticLockerInterceptor() {
        return new OptimisticLockerInterceptor();
    }
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>分别测试成功和失败案例：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">/**
     * 测试 乐观锁插件
     */
@Test
public void testOptimisticLocker() {

    //查询
    User user = userMapper.selectById(1L);
    //修改数据
    user.setName("Helen Yao");
    user.setEmail("helen@qq.com");
    //执行更新
    userMapper.updateById(user);
}

/**
     * 测试 乐观锁插件失败
     */
@Test
public void testOptimisticLockerFail() {

    //查询
    User user = userMapper.selectById(1L);
    //修改数据
    user.setName("Helen Yao1");
    user.setEmail("helen@qq.com1");

    //模拟取出数据后，数据库中version实际数据比取出的值大，即已被其它线程修改并更新了version
    user.setVersion(user.getVersion()-1);
    //执行更新
    userMapper.updateById(user);
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>实现方式总结：</p>
<p><img src="https://pluto-1300780100.cos.ap-nanjing.myqcloud.com/img/10%20乐观锁.png" alt="10 乐观锁"></p>
<h2 id="4-查询-分页"><a href="#4-查询-分页" class="headerlink" title="4.查询(分页)"></a>4.查询(分页)</h2><p>根据id查询不过多介绍，这里还需要清楚还可以通过多个id批量查询：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">@Test
public void testSelectBatchIds(){
    List&lt;User&gt; users = userMapper.selectBatchIds(Arrays.asList(1, 2, 3));
    users.forEach(System.out::println);
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>MyBatis Plus自带分页插件，只要简单的配置即可实现分页功能</p>
<p><strong>（1）创建配置类</strong></p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">/**
 * 分页插件
 */
@Bean
public PaginationInterceptor paginationInterceptor() {
    return new PaginationInterceptor();
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p><strong>（2）测试selectPage分页</strong></p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">@Test
public void testSelectPage() {

    Page&lt;User&gt; page = new Page&lt;&gt;(1,5);
    userMapper.selectPage(page, null);

    page.getRecords().forEach(System.out::println);
    System.out.println(page.getCurrent());
    System.out.println(page.getPages());
    System.out.println(page.getSize());
    System.out.println(page.getTotal());
    System.out.println(page.hasNext());
    System.out.println(page.hasPrevious());
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>测试过程中可以看到控制台sql语句打印：SELECT id,name,age,email,create_time,update_time FROM user LIMIT 0,5 </p>
<p>查询总结：</p>
<p><img src="https://pluto-1300780100.cos.ap-nanjing.myqcloud.com/img/11%20mp实现简单查询和分页查询.png" alt="11 mp实现简单查询和分页查询"></p>
<h2 id="5-删除-逻辑删除"><a href="#5-删除-逻辑删除" class="headerlink" title="5.删除(逻辑删除)"></a>5.删除(逻辑删除)</h2><p>有批量查询自然也有批量删除：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">@Test
public void testDeleteBatchIds() {
    int result = userMapper.deleteBatchIds(Arrays.asList(8, 9, 10));
    System.out.println(result);
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>在实际项目中，我们通常把删除分为实际删除和逻辑删除：</p>
<ul>
<li>物理删除：真实删除，将对应数据从数据库中删除，之后查询不到此条被删除数据</li>
<li>逻辑删除：假删除，将对应数据中代表是否被删除字段状态修改为“被删除状态”，之后在数据库中仍旧能看到此条数据记录</li>
</ul>
<p>MybatisPlus自然也提供了逻辑删除的功能</p>
<p><strong>（1）数据库中添加 deleted字段（默认为0）</strong></p>
<p><strong>（2）实体类添加deleted 字段并加上 @TableLogic 注解</strong> </p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">@TableLogic
private Integer deleted;<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre>
<p><strong>（3）application.properties 加入配置</strong></p>
<p>此为默认值，如果你的默认值和mp默认的一样,该配置可无</p>
<pre class="line-numbers language-properties" data-language="properties"><code class="language-properties">mybatis-plus.global-config.db-config.logic-delete-value=1
mybatis-plus.global-config.db-config.logic-not-delete-value=0<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre>
<p><strong>（4）在 MybatisPlusConfig 中注册逻辑删除插件Bean</strong></p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">/**
     * 逻辑删除插件
     */
@Bean
public ISqlInjector sqlInjector() {
    return new LogicSqlInjector();
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p><strong>（5）测试逻辑删除</strong></p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">/**
 * 测试 逻辑删除
 */
@Test
public void testLogicDelete() {
    int result = userMapper.deleteById(1L);
    System.out.println(result);
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<ul>
<li>测试后发现，数据并没有被删除，deleted字段的值由0变成了1</li>
<li>测试后分析打印的sql语句，是一条update</li>
<li>注意：被删除数据的deleted 字段的值必须是 0，才能被选取出来执行逻辑删除的操作</li>
</ul>
<p><strong>（6）测试逻辑删除后的查询</strong></p>
<p>MyBatis Plus中查询操作也会自动添加逻辑删除字段的判断</p>
<p>测试后分析打印的sql语句，包含 WHERE deleted=0 </p>
<p>删除总结：</p>
<p><img src="https://pluto-1300780100.cos.ap-nanjing.myqcloud.com/img/12%20mp实现逻辑删除功能.png" alt="12 mp实现逻辑删除功能"></p>
<h2 id="6-性能分析"><a href="#6-性能分析" class="headerlink" title="6.性能分析"></a>6.性能分析</h2><p>性能分析拦截器，用于输出每条 SQL 语句及其执行时间</p>
<p>SQL 性能执行分析,开发环境使用，超过指定时间，停止运行。有助于发现问题</p>
<p><strong>配置插件：</strong></p>
<p>参数：maxTime： SQL 执行最大时长，超过自动停止运行，有助于发现问题。<br>参数：format： SQL是否格式化，默认false。</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">/**
 * SQL 执行性能分析插件
 * 开发环境使用，线上不推荐。 maxTime 指的是 sql 最大执行时长
 */
@Bean
@Profile({"dev","test"})// 设置 dev test 环境开启
public PerformanceInterceptor performanceInterceptor() {
    PerformanceInterceptor performanceInterceptor = new PerformanceInterceptor();
    performanceInterceptor.setMaxTime(100);//ms，超过此处设置的ms则sql不执行
    performanceInterceptor.setFormat(true);
    return performanceInterceptor;
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p><strong>Spring Boot 中设置dev环境：</strong></p>
<pre class="line-numbers language-properties" data-language="properties"><code class="language-properties">#环境设置：dev、test、prod
spring.profiles.active=dev<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre>
<p>可以针对各环境新建不同的配置文件<code>application-dev.properties</code>、<code>application-test.properties</code>、<code>application-prod.properties</code>（之前Springboot1.x入门中提过）</p>
<h2 id="7-条件查询"><a href="#7-条件查询" class="headerlink" title="7.条件查询"></a>7.条件查询</h2><p>如果想进行复杂条件查询，那么需要使用条件构造器 Wapper</p>
<p>简单一个案例快速入门：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">/**
     * 测试 条件查询
     */
    @Test
    public void testQuery(){
        QueryWrapper&lt;User&gt; queryWrapper = new QueryWrapper&lt;&gt;();

        //ge gt le lt
//        queryWrapper.ge("age",25);

        //eq ne
//        queryWrapper.eq("name","JY");

        //between
//        queryWrapper.between("age",15,25);

        //like
//        queryWrapper.like("name","WY");

        //last  拼接到sql语句最后
//        queryWrapper.last("limit 1");

        //指定要查询的列
        queryWrapper.select("name","age");


        List&lt;User&gt; users = userMapper.selectList(queryWrapper);
        users.forEach(System.out::println);
    }<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>条件查询小总结：</p>
<p><img src="https://pluto-1300780100.cos.ap-nanjing.myqcloud.com/img/13%20mp实现复杂查询.png" alt="13 mp实现复杂查询"></p>
<h1 id="结语"><a href="#结语" class="headerlink" title="结语"></a>结语</h1><p>新年第一篇博客是在冰天雪地里写的😭</p>
<p>WDNMD没有暖气的冬天￣へ￣</p>
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                        var data_url = data.url;
                        data_url = data_url.indexOf('/') === 0 ? data.url : '/' + data_url;
                        var index_title = -1;
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});
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